The supraspinatus is a muscle located in the shoulder, involved in movement and stability. It is one of four muscles that comprise the rotator cuff, a group of muscles and tendons surrounding the shoulder joint. Understanding its precise location is fundamental to comprehending shoulder movement and why certain conditions can develop.
Precise Location of the Supraspinatus
The supraspinatus muscle is positioned on the posterior aspect of the scapula, commonly known as the shoulder blade. Its origin is the supraspinous fossa, a concave depression above the spine of the scapula. From this origin, muscle fibers gather into a tendon extending laterally. This tendon travels underneath the acromion, a bony projection from the scapula that forms the highest point of the shoulder.
After passing over the glenohumeral joint, the primary shoulder joint, the supraspinatus tendon inserts onto the superior facet of the greater tubercle of the humerus. The humerus is the long bone of the upper arm. This anatomical arrangement positions the supraspinatus as the most superior of the rotator cuff muscles.
Primary Function of the Supraspinatus
The supraspinatus muscle performs two main actions: initiating arm abduction and stabilizing the shoulder joint. Arm abduction refers to the movement of lifting the arm away from the side of the body. The supraspinatus is particularly active during the first 15 to 30 degrees of this motion, acting as the primary muscle for this initial lift. Beyond this initial range, other muscles, such as the deltoid, become more involved in continuing the abduction movement.
The muscle also contributes to the stability of the glenohumeral (shoulder) joint. It helps to keep the head of the humerus centered within the shallow glenoid cavity of the scapula. This stabilizing action prevents the humerus from slipping downward and ensures smooth, controlled movement during various arm activities. The supraspinatus works in coordination with the other rotator cuff muscles to maintain this stability during upper limb movements.
Why Its Location Matters for Health
The anatomical position of the supraspinatus makes it susceptible to certain injuries and conditions. Its tendon passes through a narrow space beneath the acromion, known as the subacromial space. This confined pathway can lead to compression of the tendon, a condition often referred to as shoulder impingement syndrome.
Impingement can result in pain, inflammation, and a reduced range of motion, particularly during overhead activities. Repetitive overhead arm movements, common in certain sports or occupations, can exacerbate this compression and contribute to the development of tendinopathy, which is the degeneration of the tendon. Additionally, both sudden trauma, such as falls, and chronic overuse can lead to partial or full tears of the supraspinatus tendon.